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Effect of pH on Protein-Binding of Orange G and Amido Black Dyes ¹

Department of Animal Science, Tennessee A. and I. State University, Nashville

ABSTRACT

The effect of pH on the absorbance of aqueous solutions of Orange G dye was negligible between pH 2.0 and 9.5. Between pH 9.5 and 11.3 there was a marked decrease in absorbance, caused by dissociation of the hydroxyl on the ß-naphthol ring. Oxalic acid has several advantages over citric acid as an acidifying agent in the dye—binding protein test of milk. Oxalic acid, used at approximately one-third the amount of citric acid, gave a lower and more reproducible pH, and increased dye-binding. It also gave complete mold inhibition. The dye-binding capacity of both casein sols and milk from individual cows was inversely related to the pH between 1.1 and 6.2.

¹ Previous article, Faculty Journal, Tennessee A. and I. State University, Nashville, January, 1962.

² Present address: Department of Dairy and Food Industry, Iowa State University, Ames, Iowa.